The present invention provides an improvement in stair module support and construction of the kind described and claimed in an earlier filed patent application and now U.S. Pat. No. 4,589,237. As disclosed in that patent installation of support systems for modular unit stairs that are prefabricated and carried to the site for installation may be substantially facilitated with considerable economy realized while affording a more stable and reliable support means relative to the prior art.
One drawback in plastic stair modules, particularly those having a substantial width, i.e., where the stair tread is about three feet or wider, is the "soft feel" or yield when a person's weight is place on the step. It is desirable that this drawback be substantially eliminated while still retaining the flexibility in the stair module which must withstand the stress of flexure and expansion and contraction.
In the invention of U.S. Pat. No. 4,589,237, the earlier difficulties of installing and leveling a stair module support system are overcome by a novel system which employs support posts in conjunction with under-the-stair plates or pads at the top of the post and shoe footings, which may include a pad, at the lower end of the post. The system of that patent provides a reliable and novel structure to facilitate installation and leveling of a stair support. That invention, as well as the present invention, has particular applicability to stair modules or shells that are formed in one piece from a suitable plastic composition and primarily those that comprise a plurality of steps and wherein the the module is supported by means at the underside of the step treads of the stair module.
While the support system of U.S. Pat. No. 4,589,237 affords a unique in system for supporting a plastic modular stair unit, the support system of that patent does not directly address the flexing in stair treads and, therefore, does not teach a means to eliminate the flexing or soft feel which the user of stairs of this kind experiences when stepping on the stairs. by a user of stairs of this kind. In other words, while some plastic compositions from which modular stair shells are molded possess the desired properties in most respects, such as desired resiliency, attractive appearance and finish, resistance to extreme weather conditions and sunlight, and the like, the yield or lack of a solid feel due to flexing when a weight is placed on the step results in an insecure or spongy sensation to one using the stairs and is objectionable for this reason.
Accordingly a need exists for an improved support system which provides the desired rigidity or solid feel to the structural unit while still permitting the use of plastic compositions that have the desired flexure properties (to accomodate easy installation), durability, appearance, economy, and the like.